Gas purifier box construction



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f?T-r'odvvfrrf 4 Sheeps-Sheet 3 G. C. PFAFF GAS PURIFIER BOX CONSTRUCTION April 7, 1953 Filed June 10. 1949 ,April 7, 1953 l l G. c. PFAFF 2,634,019

GAS PURIFIER BOX CONSTRUCTION IN V EN TOR.' Gaona: C`. PFaFF.

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Patented Apr. 7, 1953 GAS' PURIFIER BOX CONSTRUCTION George C. Pfaff, Baltimore, Md., assigner to Koppers Company, Inc., a corporation of Delaware Application June 10, 1949, Serial No. 98,320

9 Claims. (Cl. E20-71) My invention relates to an improved gas puri- `fier box of the type adapted to contain a purifying substance through which manufactured gas is passed under pressure.

As usually constructed, gas purier boxes or tanks are large closed structures in which there are removable trays on which is supported purifying material which may be a mixture of iron oxide and wood shavings. The effectiveness of the purifying material decreases with use and this material must be replaced at intervals. Accordingly, the purifier boxes are usually provided with covers which are removable so that the purifying material may be readily removed and replaced. I

These boxes are relatively large, being on the order of thirty feet square and fifteen feet high, and the gas therein is at a substantial pressure, `such as two to three pounds or more to the square inch. Because of the large area of each of the within a box, the total force exerted on a wall is considerable, and to enable the walls to withstand these forces braces have been provided between i the upper edges of the Walls on opposite sides of r'a box. These braces interfere with the removal of spent purifying material by means of mechanical devices, such as a clam shell bucket.

An object of this invention is `to provide an improved gas purier box which is arranged so that the top of the box is open and free of restrictions when the cover is removed.

A further object'of the invention is to provide an improved gas purifier box which is arranged so thatthe braces which connect the'upper parts l of opposite side walls of the box together are incorporated in the removable cover so as to be removed when the cover is removed. f, Another object of the invention is to provide an improved gas purier box which incorporates Ljoint, and having cross-braces located in fixed re.- "lation` inside the cover and removable therewith at a level above `the sealing surface and cooperside walls, and the substantial pressureof the gas Y 2 ating with' the upstanding side Wall by means in the form of brackets secured to the side walls to prevent expansion of the side Walls While the box is in service.

Another object of the invention is to provide an improved gas purifier box having side walls surrounded at the top by a reinforcing member of relatively large size and also provided at the top by a substantially at sealing surface extending completely around the box together with a cover clamped against this sealing surface, and having detachable braces associated with the cover and cooperating with brackets secured to the reinforcing member to prevent expansion of the side walls While the box is in service.

A further object of the invention is to provide an improved purifier box which is arranged so that when the cover is in place on the side walls ofthe box, the tops of opposite side walls are connected together through .braces incorporated in the cover.

Other objects of the invention and features of novelty will be apparent from the following description taken in connection with the accompanying drawings in which: Fig. 1 is an elevational View of a box embodying my invention with portions broken laway to show the interior of the box;

' Fig. 2 is a top plan view of the box shown in Fig. 1 with a portion of the cover and of the upper part of the side Walls broken away;

Fig. 3 is an enlarged fragmentary view illustrating one of the hold-down bolts employed to hold the cover in place;

Fig.'4 is an enlarged fragmentary top plan view of a tie rod bracket; u K

v Fig. 5 isan enlarged sectional view taken substantially along the line V`V of Fig. 4; A y u Fig. 6I is a fragmentary view taken substantially along the line VI--VI of Fig.. 7 and showing a modification which I may employ; and

Fig` *'7 isja sectional view taken substantiall l along the line VII-VII of Eig. 6.

Similar reference numbers refer to similar parts in each of the several views. l

The gas purier box provided by this invention is similar in construction to the boxes heretofore employed and is a large rectangular box with a surrounding upstanding side wall of substantial height in the form of sidewalls which are formed of steel plate and have vertically extending braces at intervals, while a relatively .large channel member extends around the upper edge of the side walls to reinforce them. The top edge of the A side walls has a substantially nat sealing surface material formed thereon and extending completely around the box. A removable cover is detachably secured on the top of the box and is clamped against the sealing surface to form a gas-tight joint. rihe cover has associated therewith tie rods .vhicli extend across the inside of the cover and are adapted to be secured to brackets mounted on the reinforcing member at the top of the side walls. The tie Vrods extend between opposite sidewalls and prevent expansion of the side walls by gas under pressure within the box. When the cover is removed to permit replacement of the purifying material, the pressure within the box is reduced to atmosphere and the tie rods are not required to prevent expansion ofthe side walls. As the tie rods are mounted in the cover'and'are xed thereto and removable with the cover, the top of the box is completely open'and freeof restrictions when the cover is removed. Hence, mechanical equipment, such as a crane with a clam Yshell bucket, .may be employed .to remove lthe spent purifying material and to install new When the cover is replaced, the'tie rods are also automatically replaced and are secured to the surrounding .upstanding wall as by brackets so that these tie 4rods are effective to prevent expansion of the side walls before pressure Vis built up within the box.

In a Inodication the braces within the cover are employedas partof-themeans for preventing expansion of the side walls. The cover has on its exterior projections which connect with the braces within the-cover ,and are adapted to be detachablysecured to brackets on the side walls so that opposite side walls. are connected together through the bracing in the cover.

Referring to the drawings, .the purifier box shown therein is fabricatedfrom structuralsteel and is built upon a reinforced concrete foundation [Gon which there is mountedza steeliioor plate I i. The floor plate lI covers the interiorvof the box and extendsslightiy beyond the Vside walls I2 Aof the box. rlhe side walls I2 are formed of steel plate, andeach wall is provided at intervals with vertical stifeners or lbraces I-beams I4. The lower ends ofthe I-bearns l rest on lsupporting plates i3 and are secured to the floor plate il by suitable means, as by welding, so `that Ythe iloor plate servesto connect together the Lb-earns associated with opposite side Walls of the box. The lower edges of the side ,walls I2 arealso secured to v,theeiioorplate il by suitable means, such as welding, to form la gastight `ioint.

The construction of the upper edge of .each of the side walls I2 is best shown in Figs. 3 vand 5 of the drawings. .As .therein illustrated, the upper endofeach I-beam iii `has an inner corner removed, while ahorizcnt-ally extending .channel I5 yrests on the lower part r,of -therecess in each I-beam. The channel l5 .has its :flanges .proj ect- .ing .outwardly and is mounted in ,suchrnanner that the inner face of the Web of the channel I5 is substantially in the ,same plane as the inner in the form .of i

flange ,on one of 4the .channels 2l.

4 face of the web of the channel I5 is engaged by the upper edge of the plates forming a side wall I2. The flanges on the channel I6 are on the lower face of the channel. The channel I6 is secured to the upper ends of the beams I4 by suitable means, as by welding, while the channels I5 and I6 may be welded together and the channel I5 maybe welded to the I-beams I4. In addition, the plates forming a side wall I2 are welded to thechannel l5 -to form a gas-.tight joint.

The channels I 5 and I5 extend across an entire .side of the purier box and at each end are secured `to .counterpart channels associated with an vadjoining wall. Accordingly, the upper edge of the side hwall-s vof the purier box is completely surrounded by ichannels which stiien the w-alls and prevent their deformation. The channel I5,

Abecause of its great width and the horizontal disposition -of its web, is extremely effective to prevent deformation of a wall.

Furthermore, the upper face of .the channels I l5 vprovides a substantially at, `rigid sealing sur- ,is indicated generally by the reference character 2D. The upper surface of the cover is convex between one pair .of side wallsand is substantially straight between the other pair of side walls,

Two sidesof the cover areformed of channels 2l which vhave their flanges :turned inwardly, while the other twosidesof the cover are formed ofbuilt-up members 22, each of which has on its lower edge an inwardly extending flange similar to the 'lower lflange on vone of the channels 2|. Each of the members ,22 also has on its upper edge aninwardly extending ange similar to the upper IIn addition, each of the membersZZ has a plurality of vertically disposed reinforcing members 23 extending between the upper and lower iianges on the member.

The channels `2I and the members 2-2 are secured .together at lthe corners of thecover and are arranged so .that the facesof the flanges on the lower Vedges of the vchannels 2l and of the members 22 are in substantially the same plane throughout thecircumference of the cover. The

flanges on the bottoms of the channels'ZI fand of the members 22 provide arelatively rigid, substantially nat sealing surface whichextends completely around .the cover landgis :adapted to con- .front .the sealing surface Isurrounding the v25 is secured at each end to one :of the members 22 by suitable means, as by welding.

The channels 2i on opposite sides of the cover are connected by a plurality of parallel cross- .braces 25, each of which is in the form of a plurality of sections. The sections of each brace 2t extend between oneof the channels?! and one of the braces 25, or between diiierent'braces 25,

and are connected together .through the braces 25 so as to form effective :structural ties connecting the channels 2l together. The lower faces of the braces Ei? are substantially straight, but the upper surfaces of the braces 26 are curved Vso that the upper faces of the braces 26 are substantially in the same planefas the 'upper faces 'ofthe side members 22. l

"The top of the vcover is covered by steel plate bers 22,V and the braces and 26 to form a gastight structure.

` As shown in Fig.l l of the drawings the cover is providedwith a plurality of projections which serve as hooks orpoints of attachment by means of which the cover may be lifted by a crane or hoist. The projections 30 are secured on the top of the cover at points at which the braces 25 and 26 intersect. The internal braces 25 and 26 cooperate with the side members 2| and 22 to form a rigid structure which ycan withstand the forces exerted Athereon by the gas under pressure within the box,

andy by the weight of the cover when the cover is lifted off the side walls. The internal braces 25 and 26 connect opposite sidesl of the cover together andpreventexpanson vof the side members 2| and 22 by gas under pressure within the box, while thebraces 25 and 26 prevent the plates 21 from being deformed by the gas under pressure within the box.

This purifier box is provided with means to detachably secure the cover 2|! on the box. This means comprises a plurality of hol-d-down bolts Vwhich are located a short distance apart throughout the periphery of the box.V The con- ,-f;

struction of one `of the hold-down bolts and the associated apparatus is illustrated in Fig. 3 of the drawings.

As shown in Fig. 3 of the drawings a pair of spaced vertical plates 3| are secured to the up- .per face of the channel I6 and to the outer face of the channellS. A hold-down bolt 32 having an eye at its lower end is mounted between the plates 3|, while `a pin 33 extends through aligned openings in the'plates 3| and also through the cured on a side face of the cover 2|) and have r.

substantially horizontal upper edges. 'Ihe plates forming each bracket 35 are spacedapart far enough to permit one lof the bolts 32 to move between them. A small plate 31, notched at its outer edge toreceive a bolt 32, is secured on the upper edges of the vertical plates of a bracket 35. The upper or free end of each bolt 32 is Vthreaded and is adapted to receive a cap nut 38, the lower side of which is provided with a flange which is adapted to engage the plate 31 on'abracket 35. i

The brackets 35 are secured on the cover 25 at such points that when the cover is in position on the side walls of the box a bracket 35 is located above each hold-down bolt 32. clear from Figs. 1 and 2 of the drawings,l there isa hold-down bolt 32 and a bracket 35 at each corner of the puriner box, while there are a large number of hold-down bolts on each sidewall.

As is best shown in Figs. 3 and 5 of the draw'- ings a strip oi" packing 39 is clamped between thefcover and the side walls of the box. The packing 39 may be formed of any suitable material, such as asbestos reinforced with wire,

As is 42l which is secured to the channels 2 I, the mem- Walls.

"and extends completely around the box to form a gas-tight joint between the cover and the side The packing 39 'is secured to the cover 20 by suitable rivets or bolts, the lower ends of which are countersunk in the packing.

When the box is in service, the nuts 38 on the hold-down bolts 32 are tightened down to clamp the packing strip 39 between the cover and the side walls and thus prevent escape of gas under pressure through the joint between the cover and the side walls.

The interior of the box is provided with removable trays 40 on which is supported purifying material 4| which may be a mixture of iron oxide and wood shavings. The box is also provided with inlet and :outlet connections through which gas is supplied to and discharged from the box in such manner that the gas must pass through a layer or layers of purifying material in passing through the box. The trays 40, as wellV as the inlet and outlet connections, may be arranged in any suitable well known man-A ner, and as thesev details are notnecessary to understanding of this invention, they are being omitted in order to simplify this disclosure. The cover 25 has associated therewith tie rods 42 which cooperate with brackets 43 on the side walls of the box to prevent expansion of the walls. Referring to Fig. 2 of the drawings, it will be seen that there are four tie rods 42, two rods extending in each direction across the box and being located so that the distance between each pair of rods, and between the rods and the ends or" a wall isV substantially uniform. i

Each of the rods 42 is of substantial size, such l as two inches in diameter, and is located a short distance above the lower face of the cover. Each of the rods 42 extends through aligned openings provided in the braces 25 and 26, and is ofsuch length that the ends of the rod project from the sides of the cover a short distance, as shown in Fig. 5. The joints present where the rods 42 pass through the side walls of the cover are sealed by welding the rods to the cover. i

Each of the side walls is provided with brackets indicated generally by the reference character 43 and adapted to receive the projecting ends of the tie rods 42. Referring to Figs. 4 and 5, it will be seenthat the channel i6 has an opening therethrough and that a member"45 extends through this opening. The lower end of the member 45 engages the inner face ofV a channel 41 which extends between adjacent ,I beams I4 and is secured to these I-beams as well as to thelower face of the channel l.

The portion of the member 46 which extends above the channel I6 is bifurcated and has a slot therein of suchl width as tofreely receive the end ofla rod 42. A pair of spaced angular reinforcing members 48 are secured to the upper face of the channel I6 and extend between the member 45 and the channel l5, the members 4B being welded to the member 45 and tc the chan nels 5 and I6: As is clearly shown in Fig. 5 the members 48 are cut to fit the space between the channel I5 and the upper iiange of the channel I5, while the members 48 extend away from the channel l5 so as not to interfere with the cover 2u. Asis clearly shown in Fig.` 4, the braces 43 are spaced apart far enough that theupper ends of these members are not engaged by the tie rod 42. g i A single, substantially triangular reinforcing 1nember5|lextends between the outer faceY of tha-member l andA the upper 'face of: the channel 1.6i. As showny in li'g.v 5.l the. member 5c isv of `srxclr vertical height that it does. not extend above the bottom of: the: slot in the' member 45. and therefore does not interfere with. the tie rod. 42, nor with the nut on the end of the tie rod. As `shown in Fig. 4 the reinforcing member 5t. is located' centrally of. theY member 46 and. issub.- stantially in alignmentl with the slot or; recess in 'themember 46; The. reinforcing member; 56 is secured to the channel It and tothe member 46 by. welding. y

The free end ofv each of the tie rods. 42. is threaded and has mounted thereon a. nut 5| which engages the face ofthe memberl 45..

' Eachl end of each tie rod 42 has a nut 5,! thereon and when thel nuts on opposite ends of a tie rod are tightened, the opposite side` walls 'are drawn together and are thereafter prevented from expanding by the tie rods 42 which are un.- der tension. The force exerted on the side walls bythe gas under pressure within the purifier box causes the tension on the tie rods 42 to beincreased, while force is exerted on the brackets 43 tending to-move the upper end of each bracket inwardly, and to move the lower end of each bracket outwardly. However, the braces 48' and 50 prevent inward movement of the upper end of each bracket 43, while the channels 4l, which are secured to the I-beams i4, prevent outward movement of the lower end of each bracket. Hence, the brackets 43 are extremely rigid and effectively transmit force between the side walls and the tie rods. In addition, it will be seen that the brackets 43 are mounted on and' are f placed, the box is taken out of service', and the L pressure of the gas within the box isA reduced to atmospheric' pressure with the result that force is no longer exerted on the side walls of the box tending to expand them. The nuts 38 on the hold-down bolts 32 are now loosened, each nut beingV loosened enough to permit the associated boltto be swung free of the bracket 35. The nuts 5|f on the tie rodsv 42 are also loosened, and the cover is lifted` from the top of the box by acrane or hoist, not shown, and is removedf'rom above the box. When the cover is lifted off the side Walls of the box, the tie rodsy 42 are lifted out of. the slots or recesses in the brackets 43. The top of the box is now completely open and unobstructed so that mechanical equipment may be employed to remove and replace the purifying material. maybe removed and replaced with a minimum of diiiculty.

After the new purifying material has been installed, the cover 20 is brought to a position above the side walls of the box and is then lowered so that the ends of the tie rods 42 are received in the slots or recesses in the brackets 43. At this time the sealing surface surrounding the lower face ofthe cover 20 rests on the gasket 39, while the gasket 39 rests on the upper face of the channels IE.

The hold-down bolts 32 are now swung upwardly to their vertical positions, and the nuts In addition, the removabletrays 4I!` 38- are tightened. to. draw the cover 2i! down-and clamp the gasket 39 between the' cover andthe side. walls. In addition, thenuts. 5l on the ends of the tie rods.42 are tightened to build up an initial tension on the tie rods andv prevent subsequent expansion of the side walls.

The box is now ready to be placed in service and when the pressure of the gas withinthebox is built up, force is exerted on the side walls tending to expand them, loutV their expansion is prevented by the tie bolts 42.

It will bevseen thatA expansion of the upper edge portion of the side walls of the box by the gasl under pressure within the boxV is prevented by tie rods extending between opposite side walls. These tie rods are incorporated in the cover and are removed when the cover is removed. Hence, when the cover is removed, the tie rods are removed and the upper face of the box is unu obstructed. When the cover is removed, the gas within the box isv no longer underv pressure and the tie rods are not required to prevent expansion of the side walls. The cover must be replaced before the pressure within the box can be built up, and as the tie rodsA are replaced when the cover is replaced, thetie rods are effective wheny theyv are needed.

In the species heretofore described specialv tie rods arel incorporated in the cover and serve to connect the upper edges of'oppositeside walls together. It is not necessary to provide special tie rods for this purpose asthe internal bracing in the cover may be employed for this purpose, and Figs. 6 and' 7` illustrate thismodification.

Referring to Figs. 61 and 7 of the drawings il? will be seen that the cover Za has secured t0 thel exterior thereof' a projection 6D which is in the form of a vertically disposed plate. The member G is mounted' on the side of the cover in alignment with one of the internal braces, such as a brace 26a, extending across the inside of the cover. Each of the members 60 is secured to the exterior'of the coverin such manner as to be connected directly7 to the associated brace within the cover. As shown in the drawings the interior brace 26a has angles 62 at the end which. engage the inner face. of the channel 2|. The projection 66 is provided with similar angles 63 which. engage the outer face of the channel 21.. The angles E2. and B3. are secured together by. rivets. S4 which extend through the channel 2l. The free end of eachprojection 60 is. adapted to. extend. through the slot or recess in the. top. of abracket 43a, which is similar t0 the.. bracket illustratedand described in connection withthe tie rods. The free endof each projection. 60 has therein a rectangular slot or opening 65 which is located so that most, but not all, ofv this slot is beyond the outer face Of the bracket 43a. The slot 65 is adapted toreceive a wedge i'v While the outer face of the bracket' 43ahastherein a groove S13, which is somewhat wider than the slot` 65 or the wedge 57.

A wedge 6T is inserted in a slot 65 and is driven tight by suitable means, such as a Sledge hammer; with. the result that the outer face of the wedge exerts force on the outer edge of the slot 65 in the projection B to exert tension on the projection and thus exert tension on the associated brace within the cover;

Each side ofthe cover 26a is provided with a plurality of projections 6!) which are spaced apart throughout the length of that side ofthe cover so that opposite side walls of the box are connected together through rality of places. Y

When the cover is to beremoved, the wedges 61 are removed and after the hold-down bolts have been released, the cover may be lifted olf. When the cover is to be replaced, the cover S placed on the` box so` that the projections 6E! enter the slots in the tops of thebrackets 43a. After the hold-down bolts have been tightened, the 'wedges 61 are inserted and driven tight. Thereafter, the side walls are prevented from expanding because the side walls are connected together through the braces in the cover, This modification, like that heretofore described, provides means associated with the cover for preventing expansion of the upper parts of the side walls while the box is in service, whilethis'means is arranged so that when the cover isgremoved, the top of the box is completely unobstructed.

Furthermore, itwill be seen that bothlmodicationsyof the box .provided by this invention are arranged so that .the means for connecting opposite side Walls together when the cover is inplace are completely independent of. the sealing surfaces on the cover and side Walls. Hence, the sealing surfaces remainflat surfaces and provide an eifective seal between the cover and the 'side walls. 'AlthoughfIhave herein illustrated two'forms ofmimproved` gas-.purifier box embodying my invention, it should be understood that the irlvenu tion is not limited to these details of constructhe cover Vat a plu- Vtion and that numerous modifications and changes may be made without departing from the spirit and scope of the following claims.

`Having thus described my invention, what I claim is:

,1. In a gas purifier box of the type described having pairs of substantially parallel side Walls and having a cover with means for detachably securing the cover on the top of said side walls with a tight seal, the combination of tie rods for preventing outward movement of the upper edges of said side walls by gas under pressure withinV the box while leaving the upper face of the box completely unobstructed when the cover is removed, and brackets secured on said side walls, said tie rods extending across said cover on the inside thereof and being fixed thereto for removal therewith, said tie rods having their ends projecting from said cover in position to fit into said brackets, at least one tie rod GX- tending between each opposite pair of side walls, and means for detachably securing the ends of said tie rods to said brackets when said cover is in position on said side walls.

2. In a purier box of the type having substantially parallel side Walls and having a, cover with means for detachably securing the cover on the top of said side walls', the combination with the foregoing apparatus of means for preventing outward movement of the upper edges of said side walls by gas under pressure within the box while leaving the upper face of the box completely unobstructed when the cover is removed, said means comprising tie rods extend- Aing across said cover and having their ends projecting from said cover, at least one tie rod extending between each opposite pair of side walls, and means for detachably connecting the ends of said tie rods with said side walls, said last named means comprising brackets mounted on said side walls and having therein recesses having substantially parallel side Walls, a cover detachably secured on said side walls, said cover and said side walls being surrounded 'by sealing surfaces which confront each other when the cover is in position on said side walls, tie rods extending across said cover and having their ends projecting through the sides of said cover above the sealing surface on said cover, at least one tie rod extending between each opposite pair of side wallsfand means for detachably securing the ends of said tie rods to said side walls. 1

4. In apparatus ofthe class described, a box having substantially parallel side walls, a cover withmeans for-detachably securing it on said side Walls, said cover and said side walls being surrounded by sealing surfaces which confront each other when the cover is in position on said side walls, said cover including cross-braces which extend between opposite pairs of sides of said cover, said cover having on each side thereof at least one projecting member which extends outwardly from said cover, the projecting Lmembers on opposite sides of said cover beingconnected together through one of said cross-braces, and means for detachably connecting said projecting members to said side walls.

5. In apparatus of theclass described', a box having substantially parallel side walls, acover having means for detachably securing it on top of said side walls, said cover and said side walls being surrounded by sealing surfaces which confront each other when the cover is in position on said side walls, said cover including crossbraces which extend between opposite pairs of sides of said cover, said cover having on each side thereof an external projection located substantially in alignment with one of said cross-braces, the projections associated with opposite side walls being substantially in alignment with the same cross-brace and being connected together through such cross-brace, and means for detachably securing said projections to said side walls.

6. In apparatus of the class described, a box having substantially parallel side walls, a cover detachably secured on said side Walls, said cover and said side walls being surrounded by sealing surfaces which confront each other when the cover is in position on said side Walls, clamping means for detachably connecting the cover in sealing position on the side walls, each of said side walls having secured thereon adjacent its upper edge a bracket having a recess opening on its upper face, and means extending across said cover with end members extending through the recesses in said brackets when the cover is in position on said side walls for preventing outward movement of said side walls by fluid under pressure within said box.

7. In apparatus of the class described, a box having substantially parallel side walls, a cover Y detachably secured on said side walls, said cover and said side walls being surrounded by sealing surfaces which confront each other when the cover is in position on said side walls, clamping means for detachably sealing said cover on top of said side walls, each of said side walls having secured thereon adjacent its upper edge a bracket which extends above the sealing surface on said side wall and has in the portion above said sealing surface a recess opening on the upper face of said bracket, and means carried by said cover and extending through the recesses in said brackets when the cover is in position on said side walls for preventing outward movement of said side walls by fluid under pressure Within said box.

8. In apparatus of the class described, a box having substantially parallel side walls, a cover detachably secured on said side Walls, said cover and said side walls being surrounded by sealing surfaces which confront each other when vthe cover is in position on said side walls, clamping means for detachably sealing said cover on the top of said side walls, each of said side Walls having secured on the outer face thereof a bracket which extends above the sealing surface on said side wall and has in the portion above said sealing surface a recess opening on the upper face of said bracket, projections on said cover which extend through the recesses Vin said brackets when the cover is in position on said side Walls, and means within the cover and connecting together the projections-on opposite sides vof said cover.

9. In a gas purier boxof the type described, having a surrounding upstanding side wall and having a removable rcover with means for detachably securing the cover on the top of said side wall with a tight seal, and cross braces for preventing outward expansion movement of the upper edges of said surrounding side Wall by gas under pressure within the box, the improvement characterized by `said cross braces extending across the inside of the cover and being xed 12 thereto for removal with the cover, and Vbrackets xed to said surrounding side wall, 'sai'd cross braces having ends projecting from said cover in position to t into said brackets xed to said surrounding side wall, and means for detachably securing the projecting ends of said cross braces to said brackets 'when said cover is in position on top of said box `side wall.

GEORGE C. -PFAFF- f REFERENCES CITED The following references are of record in the flle of this patent:

UNITED lSTATES PATENTS Number Name Date 368,844 McCormick. Aug. 23, 1887 584,068 Weber June 8, 1897 658,343 Clark Sept. 25, 1900 781,080 Lynch Jan. 31, 1905 814,160 Paige Mar. 6, 1906 1,140,414 Steel May 25, -1915 1,144,159 Truxall June 22, 1915 1,645,171 Weiss Oct. 11, 1927 1,672,904 Randall June 12, 1928 1,733,004 Bower Oct. 22, 1929 2,037,707 Davis et al Apr. 21, 1936 2,130,287 Nooney Sept. 13, 1938 2,448,031 Johnson et al Aug. 31, 1948 2,452,931 Jacob v Nov. 2, 1948 

